284 
PALAEONTOLOGY OF NEW-YORK. 
Athyris spiriferoides. 
The origin of the crura, or point of attachment to the hinge-plate, is 
indicated in the figure at a, from which the two lamellse proceed for a 
short distance in a nearly direct line forward, but are soon bent upwards 
and recurved upon themselves as shown in the figure at b, whence they 
are again bent downwards into the cavity of the dorsal valve. From this 
point the lamellae follow very nearly a direction parallel to the external 
contour of the shell, being the exterior bands indicated by the dotted 
lines to c. Farther on, these become expanded and send off from each one 
a projecting process at d, and thence are united “in a solid plate at e, 
forming the loop which connects the two parts of the spiral arms. It will 
also .be observed that the lamellae are twisted, the exterior part at d 
becoming the interior at the point of junction of the two parts. This 
plate, formed by the junction of the lamellae, is sharply bent backwards 
almost in the plane of the longitudinal axis of the shell; and thence ris¬ 
ing nearly at right angles, becomes bifurcated at /, giving origin to the 
accessary lamellae g, which are recurved in a plane essentially parallel 
to the first volution of the spire, and coalesce with it at the points indi¬ 
cated by the dotted lines h, thus acting as an additional support to the 
# I am indebted to the rare mechanical skill and artistic manipulation of Mr. R. P. Whitfield for 
the preparation of specimens illustrative of this and another species of Athyris, as well as of the 
spires of Meristella, etc. 
